Method of making multilayer printed circuit board

Abstract

A multilayer printed circuit board in which multiple layers of a composite material, fabricated by the lay-up of an aramid fiber tape, are employed to provide a circuit board with a desired coefficient of thermal expansion. Tape lay-up of aramid fibers provides a composite layer having a lower thermal coefficient of expansion than a composite layer fabricated from woven aramid fibers. Degradation in the tensile modulus of elasticity caused by the over and under characteristics of woven fabrics is also eliminated by tape lay-up, thus providing a circuit board with better mechanical strength. In addition, tape lay-up reduces the amount of resin required to fabricate the circuit board and eliminates the need for twisting the aramid fibers into yarns and then weaving the yarns, thus reducing the cost of the circuit board.

I claim: 
     
       1. A method for fabricating a multilayer printed circuit board, comprising the steps of: forming a plurality of layers of a composite material by lay-up of an aramid fiber tape, each composite layer including a plurality of layers of the aramid fiber tape;   plating at least one side of some of the composite layers with a layer of copper;   etching the copper layers with predefined circuit patterns; and   laminating the composite layers with insulating adhesive layers to form a printed circuit board having a coefficient of thermal expansion that is approximately equal to that of the electrical components to be mounted on the circuit board.   
     
     
       2. A method for fabricating a multilayer printed circuit board as set forth in claim 1, wherein each composite layer includes two outer layers and two inner layers of the aramid fiber tape, the aramid fiber tape being oriented in the X direction in the outer layers and in the Y direction in the inner layers. 
     
     
       3. A method for fabricating a multilayer printed circuit board as set forth in claim 1, wherein the aramid fiber tape is a single layer of aramid fibers coated with a resin and heated to a semi-cured stage. 
     
     
       4. A method for fabricating a multilayer printed circuit board as set forth in claim 1, wherein the insulating adhesive layers are each a single layer of aramid fiber tape. 
     
     
       5. A method for fabricating a multilayer printed circuit board as set forth in claim 1, wherein the insulating adhesive layers are each a single layer of woven aramid fibers impregnated with a resin. 
     
     
       6. A method for fabricating a multilayer printed circuit board as set forth in claim 3, wherein the resin is an epoxy resin. 
     
     
       7. A method for fabricating a multilayer printed circuit board as set forth in claim wherein the resin is a polyimide resin. 
     
     
       8. A method for fabricating a multilayer printed circuit board, comprising the steps of: forming a plurality of layers of a composite material by lay-up of a fiber tape, each composite layer including a plurality of layers of the fiber tape;   plating at least on side of some of the composite layers with a later of conductive metal;   etching the metal layers with predefined circuit patterns; and   laminating the composite layers with insulating adhesive layers to form a printed circuit board having a coefficient of thermal expansion that is approximately equal to that of the electrical components to be mounted on the circuit board.   
     
     
       9. A method for fabricating a multilayer printed circuit board as set forth in claim 8, wherein each composite layer includes two outer layers and two inner layers of the fiber tape, the fiber tape being oriented in the X direction in the outer layers and in the Y direction in the inner layers. 
     
     
       10. A method for fabricating a multilayer printed circuit board as set forth in claim 8, wherein the fiber tape is a single layer of fibers coated with a resin and heated to a semi-cured stage. 
     
     
       11. A method for fabricating a multilayer printed circuit board as set forth in claim 8, wherein the insulating adhesive layers are each a single layer of fiber tape. 
     
     
       12. A method for fabricating a multilayer printed circuit board as set forth in claim 8, wherein the insulating adhesive layers are each a single layer of woven fibers impregnated with a resin. 
     
     
       13. A method for fabricating a multilayer printed circuit board as set forth in claim 10, wherein the fiber is an aramid fiber. 
     
     
       14. A method for fabricating a multilayer printed circuit board as set forth in claim 10, wherein the resin is an epoxy resin. 
     
     
       15. A method for fabricating a multilayer printed circuit board as set forth in claim 10, wherein the resin is a polyimide resin. 
     
     
       16. A method for fabricating a multilayer printed circuit board as set forth in claim 8, wherein the conductive metal is copper.